Oxygen conservation system for commercial aircraft

ABSTRACT

An emergency oxygen supply system for use on aircraft in the event of a loss in cabin pressure is configured for delivering allotments of oxygen and timing the delivery such allotments to each passenger so as maximize the efficiency of the transfer of such oxygen into the passenger&#39;s bloodstream. The delivery of each allotment is selected so that the entire allotment is available for inhalation into the region of the lung most efficient at oxygen transfer while the volume of the allotment is selected to substantially coincide with the volume of such region of the lung.

FIELD OF THE INVENTION

The present invention generally relates to emergency oxygen supplysystems such as are routinely carried on commercial aircraft fordeployment upon loss of cabin pressure. More particularly, the inventionpertains to enhancing the efficiency with which the supplied oxygen isused to thereby reduce the total amount of oxygen that needs to becarried on an aircraft.

BACKGROUND OF THE INVENTION

Emergency oxygen supply systems are commonly installed on aircraft forthe purpose of supplying oxygen to passengers upon loss of cabinpressure at altitudes above about 12,000 feet. Such systems typicallyinclude a face mask adapted to fit over the mouth and nose which isreleased from an overhead storage compartment when needed. Supplementaloxygen delivered by the mask increases the level of blood oxygensaturation in the mask user beyond what would be experienced if ambientair were breathed at the prevailing cabin pressure altitude condition.The flow of oxygen provided thereby is calculated to be sufficient tosustain all passengers until cabin pressure is reestablished or until alower, safer altitude can be reached.

Each such face mask has a reservoir bag attached thereto into which aconstant flow of oxygen is directed upon deployment of the system andupon activation of the individual face mask via a pull cord. The oxygenis supplied continuously at a rate that is calculated to accommodate aworst case scenario, namely to satisfy the need of a passenger with asignificantly larger than average tidal volume who is breathing at afaster than average respiration rate when cabin pressure is lost atmaximum cruising altitude. A total of three valves that are associatedwith the mask serve to coordinate flows between the bag and the mask,and between the mask and the surroundings. An inhalation valve serves toconfine the oxygen flowing into the bag to the bag while the passengeris exhaling as well as during the post-expiratory pause and at all timesalso prevents any flow from the mask into the bag. When the passengerinhales, the inhalation valve opens to allow for the inhalation of theoxygen that has accumulated in the bag. Upon depletion of theaccumulated oxygen, the dilution valve opens to allow cabin air to bedrawn into the mask. The continuing flow of oxygen into the bag andthrough the open inhalation valve into the mask is thereby diluted bythe cabin air that is inhaled during the balance of the inhalationphase. During exhalation, the exhalation valve opens to allow a freeflow from the mask into the surroundings while the inhalation valvecloses to prevent flow from the mask back into the bag. All three valvesremain closed during the post-expiratory pause while oxygen continues toflow into the reservoir bag.

Inefficiencies in an emergency oxygen supply system can require theoxygen storage or oxygen generation means to be larger and thereforeweigh more than necessary which of course has an adverse impact on thepayload capacity and fuel consumption of the aircraft. Enhancing theefficiency of such a system either in terms of the generation, storage,distribution or consumption of oxygen could therefore yield a weightsavings. Conversely, an enhancement of a system's efficiency without acommensurate downsizing would impart a larger margin of safety in thesystem's operation. It is therefore highly desirable to enhance theefficiency of an emergency oxygen supply system in any way possible.

SUMMARY OF THE INVENTION

The present invention overcomes shortcomings inherent in emergencyoxygen supply systems that are currently in use on commercial aircraftto substantially reduce the amount of oxygen that is needed in the eventof a loss in cabin pressure. The need to carry or generate less oxygenon board allows a significant weight savings to be realized.Alternatively, foregoing a reduction in the size of the oxygen supplyallows the system to operate with an enhanced margin of safety.

The reduction in the rate of oxygen consumption is achieved by adjustingthe allotment of oxygen to each individual passenger as function of suchpassenger's actual demand therefor and by in effect inducing thepassenger to more efficiently use such allotment. More particularly,allotment is adjusted as a function of each passenger's respiration ratewherein faster breathing results in a faster delivery rate of thepassenger's oxygen allotments. More efficient use of the deliveredoxygen is induced by timing the delivery of oxygen so that it is inhaledinto the most absorption efficient region of the lung and by limitingthe volume of the delivered oxygen so as to approximately coincide withthe volume of that region of the lung. Cabin air is relied upon tofulfill the balance of the passenger's respiratory volume.

The present invention takes advantage of the fact that while someregions of the lung are more effective at transferring oxygen to theblood than others, the region of the lung with the highest efficacy isfirst to be filled during the inhalation phase. Such region comprisesthe lower lobes of the lungs and accounts for approximately one third ofthe volume inhaled during a typical breath. The upper lobes of the lungare next to fill during the inhalation phase, account for another onethird of the volume inhaled during a typical breath and are onlymoderately effective at transferring oxygen to the blood. The final onethird of the volume inhaled during a typical breath comprises thetrachea and bronchi which have essentially no oxygen transfercapability. By ensuring that a volume of supplemental oxygen that isinhaled is delivered to the respiratory tract immediately upon start ofthe inhalation phase, maximum efficiency can be achieved. Deliveringsaid supplemental oxygen in the most efficient manner serves to minimizethe volume that must be delivered.

The minimum needed volume of supplemental oxygen can be determinedempirically for a given dispensing device and cabin pressure altitude bythe following general means:

A human subject is placed in an altitude chamber and the subject isfitted with a pulse oximeter or other suitable instrumentation tomeasure the level of blood oxygen saturation. Oxygen is deliveredinitially via the selected dispensing device at a rate known to be safewithout taking into consideration the benefit that results fromdispensing the oxygen at the most effective point in the breathingcycle. The dispensing rate is then gradually adjusted downward whileobserving the effect of changed oxygen dosage on the subject's bloodoxygen saturation. When the blood oxygen saturation reaches the minimumvalue considered safe under the test conditions, this is considered theminimum dosage for said conditions of pressure altitude and dispensingdevice configuration. This experiment is repeated at various altitudesusing various test subjects until sufficient data is accumulated to showthe necessary minimum dosage as a function of altitude for thepopulation from which the test subjects are drawn.

The minimum blood oxygen saturation level considered acceptably safe isa matter of scientific judgment, depending on such factors as the degreeof safety sought and the characteristics of the population to beafforded protection. Under a standard that has been applied previouslyin certifying passenger oxygen equipment for civil aviationapplications, a blood oxygen saturation equal to that achieved when thetest subject is breathing ambient air at a pressure altitude of 10,000ft to 14,000 ft would be considered safe for a limited duration exposureof the sort that would be encountered during an emergency following aloss of cabin pressurization.

In order for an allotment of oxygen to be available for inspiration inevery breathing cycle, a preselected event during the respiratory cycleis relied upon to trigger the delivery of oxygen. The most preferredsuch event is the beginning of the exhalation phase as it is easilydetected and gives the system the maximum amount of time to transmit theallotment of oxygen to the passenger. Because the volume of each oxygenallotment is the same for each passenger, a passenger's respiratory rateshould be expected to rise in the event the allotment initially fails tosatisfy a particular passenger's oxygen requirement. Conversely, apassenger's respiratory rate would be expected to decrease should theoxygen allotment exceed such passenger's oxygen requirement. If desired,deployment of the oxygen masks could be used as a trigger to deliver theinitial charge of oxygen to the reservoir, in preparation for the user'sfirst inhalation.

In a preferred embodiment of the present invention, the emergency oxygensupply system employs a slightly modified version of the oronasal facemask and reservoir bag combination that is currently used to the extentthat a pressure sensor is fitted to each face mask. The pressure sensoris configured to detect a pressure increase within the mask such asoccurs upon exhalation. Additionally, an inlet valve is fitted to theoxygen supply line for each reservoir to control the flow of oxygenthereinto. The ability to adapt a substantially conventional face maskfor use with the system of the present invention is especiallyadvantageous as the user interface, with which the passengers arefamiliar to the extent that the mask is demonstrated before everyflight, remains unchanged.

In an alternative embodiment, the pressure sensor can be located at adistance from the mask and a tube or duct that communicates between themask and the sensor can be provided. The presence of exhalation pressurein the mask would produce a corresponding increase in pressure in theduct that would be transferred to and sensed by the remotely locatedpressure sensor. This embodiment would permit the sensor to be mountedin a fixed location near the oxygen source, reducing the weight of themask that interfaces with the user's face, and protecting the sensorfrom mechanical shocks that the mask could experience.

A calculating device such as a microprocessor, which serves as acontroller, receives input from each of the mask pressure sensors aswell as additional input such as from sensors that measure the ambientpressure within the cabin to determine the timing of the opening andclosing of each inlet valve. In the preferred embodiment, each inletvalve will open when the beginning of an exhalation is detected in theassociated mask. The valve will be closed a short time thereafter,wherein the timing thereof is a function of the detected ambientpressure so that altitude can be compensated for. An allotment of oxygenwill be delivered to each passenger's reservoir bag during suchpassenger's exhalation phase while the size of the allotment will beadjusted as a function of altitude—the higher the altitude, the largerthe allotment.

In another preferred embodiment, the pressure sensor associated witheach mask is relied up to provide the information necessary to estimatethe passenger's tidal volume. This estimate can be made by consideringthe magnitude of exhalation pressure, which would be indicative of therelative rate of flow through the exhalation valve, and the durationduring which exhalation pressure is present. By adjusting the timing ofthe closing of the inlet valve so as to permit a volume of oxygen toenter the reservoir bag that substantially coincides with the desiredfraction of the passenger's tidal volume even greater efficiencies canbe achieved as both the timing and volume of a passenger's oxygen demandcan thereby be closely matched.

In an alternative embodiment, the triggering event for delivery ofoxygen to the mask could be the onset of inhalation. In that case, therate of oxygen delivery to the mask would preferably exceed the initialinhalation rate, to ensure the desired volume of oxygen is dispensed tothe reservoir bag soon enough to be available for inhalation during thepreferred initial portion of the inhalation cycle.

In an alternative embodiment, the controller can track the time betweentrigger signals from a given mask. In the event the time elapsed since atriggering event exceeds a predetermined threshold value, the inputvalve could be signaled to open, delivering an increment of oxygen.Although this increment would not arrive at the optimum time in thebreathing cycle, this feature would provide some level of protectionagainst the possibility that the pressure sensor failed to detect thetriggering event.

In a preferred embodiment, the oxygen supply is carried in pressurizedcylinders rather than generated when needed. This obviates the need foran ignition system, does not involve the generation of heat nor residue,while the downstream pressure is easily regulated and flow is easilymodulated. Additionally, a simple pressure gauge allows the readiness ofthe system to be continually monitored wherein a low cylinder is readilyidentifiable and easily replaced to restore the system to fulloperability.

These and other advantages of the present invention will become apparentfrom the following detailed description of preferred embodiments which,taken in conjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic illustration of an oxygen mask for use in theemergency oxygen supply system of the present invention; and

FIG. 2 is a schematic illustration of the emergency oxygen supply systemof the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The Figures illustrate a preferred embodiment of the present invention.The emergency oxygen supply system provides for enhanced efficiencies inthe distribution and consumption of the oxygen that is carried aboard anaircraft for use in the event of a loss in cabin pressure. Upondeployment of the system, oxygen is distributed to individual passengersas a function of each individual passenger's respiration rate. Thedelivery of each allotment of oxygen to each passenger is timed so as toensure that it is inhaled into that region of the lung that is mostefficient at transferring oxygen into the blood while the volume of eachallotment is selected to coincide with the approximated volume of suchregion of the lung.

FIG. 1 is a schematic illustration of the user interface 12 of thepresent invention. An oronasal mask 14 is configured to fit against apassenger's 16 face and is held in place by an elastic band 18 thatextends about the back of the head. An inflatable reservoir bag 20 isattached to the mask and is in fluid communication with a supply conduit22 through which the flow of oxygen into the bag is controlled by inletvalve 24. The mask includes an inhalation valve 26 that is configured toallow oxygen that has accumulated in the bag to be drawn into the maskduring inhalation and to prevent any flow from the mask into the bag.The mask additionally includes a dilution valve 28 that is configured toallow ambient cabin air to be drawn in the mask only after the bagcontents has been depleted. The mask also includes an exhalation valve30 that is configured to allow an exhaled breath to be expelled into thecabin. A pressure sensor 32 fitted to the mask generates a signal when apositive pressure is detected within the mask such as is caused byexhalation. A controller 34 receives input from the pressure sensor andserves to open and close the inlet valve.

FIG. 2 is a schematic illustration of the emergency oxygen supply system36 of the present invention. One or more cylinders 38 of compressedoxygen serve to store the required supply of oxygen. A regulator 40reduces the pressure of oxygen that is distributed to the individualuser interfaces 12 via a network of conduits 42, wherein the flow ofoxygen to each individual reservoir bag 20 is controlled by therespective inlet valve 24. A controller 34 receives input from eachindividual pressure sensor 32, as well as a host computer 44 which inturn receives input from pressure sensors 46 that monitor ambientpressures within the cabin as well as input from the controller and fromthe flight deck via bus 48.

In use, the readiness of the oxygen supply is easily verifiable bymonitoring the internal pressure of cylinder 38. Should a substandardpressure be detected, the oxygen cylinder is either replaced or toppedoff. When a loss of cabin pressure occurs, all passenger interfaces 12are released from overhead storage compartments and a pressure regulatedsupply of oxygen is released into the distribution network 42.Activation of an individual passenger interface is accomplished byselecting a face mask 14 and breathing thereinto. An exhalation isdetected by sensor 32 which causes controller 34 to open the inlet valve24 that is associated with the face mask to allow the influx of oxygeninto the associated reservoir bag 20. The controller calculates thevolume of oxygen needed in light of the ambient cabin pressure andcloses the inlet valve after an appropriate period of time. The system'soxygen pressure is preferably regulated to a level such that the desiredvolume of oxygen is deliverable to the reservoir bag well within theperiod of time needed for exhalation. During the passenger'spost-expiratory pause, the delivered oxygen is held in the reservoirbag. Upon inhalation, the inhalation valve 26, shown in FIG. 1, allowsall of the oxygen within the reservoir bag to be inhaled to fill thepassenger's lower lung lobes where the most efficient oxygen transfertakes place. Upon depletion of the contents of the reservoir bag,further inhalation causes the mask's dilution valve to open so as toallow the passenger's respiratory demand to be satisfied by ambientcabin air. Exhalation causes the sequence to repeat.

The configuration of the system causes the frequency with which eachreservoir bag is filled to match the frequency of the respiratory rateof the passenger breathing therefrom. Should the volume of oxygen thatis received by a particular passenger fail to satisfy that particularpassenger's oxygen demand, the respiratory rate would be expected toincrease to thereby increasing the frequency with which the allotmentsof oxygen are delivered to the passenger. Conversely, should the volumeof oxygen that is received by a particular passenger during eachrespiratory cycle exceed such passenger's oxygen requirement, thepassenger's respiratory rate would be expected to decrease, therebydecreasing the net flow of oxygen to the passenger.

Within the scope of this invention, the quantity delivered couldoptionally be increased above the absolute minimum needed, in order toprovide a safety margin, if desired.

By timing the delivery of oxygen to each passenger such that the entireoxygen allotment is available for inhalation immediately uponcommencement of the inhalation phase, the delivered supplemental oxygenis inhaled into the region of the lung that is most efficient attransferring oxygen to the blood. Because the supplemental oxygen isdelivered in the most efficient manner, the quantity of supplementaloxygen needed to achieve a given, desired degree of blood oxygenation isminimized.

Reliance on compressed oxygen rather than chemical oxygen generatorsallows the net flow of oxygen throughout the distribution network to bematched to the net demand for oxygen without having to accommodate abuild up of pressure or heat. The readiness of a compressed oxygensupply, i.e. the cylinder pressure, is also much more easily verifiedthan the readiness of a solid chemical and ignition system. The costlyand time consuming need to periodically replace a multitude of oxygengenerators is thereby completely obviated.

By substantially matching the delivery of oxygen to a passenger's demandtherefor, the efficiency of an emergency oxygen supply system ismaximized and oxygen consumption is minimized. Such an increase inefficiency allows the size of the oxygen supply to be reduced whencompared with less efficient systems such as are currently in use andthereby allows a substantial weight reduction to be realized. The weightreduction in turn translates into a reduction in an aircraft's fuelconsumption and/or an increase in payload capacity.

While particular forms of this invention have been described andillustrated, it will be apparent to those skilled in the art thatvarious modifications can be made without departing from the spirit andscope of the invention. Accordingly, it is not intended that theinvention be limited except by the appended claims.

1. An oxygen supply system for delivering oxygen to passengers in anaircraft in the event of a loss of cabin pressure, comprising: a sourceof oxygen; a reservoir bag for accumulating a volume of oxygen flowingfrom said source; a face mask configured to force a passenger wearingsaid mask to inhale said accumulated volume of oxygen from saidreservoir bag prior to allowing said passenger to inhale cabin airduring each respiratory cycle; and an inlet valve for limiting the flowof oxygen into said bag to a period of time during each respiratorycycle that is sufficient to allow only a preselected volume of oxygen toaccumulate in the bag.
 2. The oxygen supply system of claim 1, whereinsaid preselected volume of oxygen comprises a volume of oxygensufficient to maintain a preselected oxygen saturation level in apreselected population of passengers at a prevailing cabin pressurealtitude.
 3. The oxygen supply system of claim 1, wherein said inletvalve remains closed during a passenger's inhalation phase.
 4. Theoxygen supply system of claim 3, wherein said inlet valve is openedduring a passenger's exhalation phase.
 5. The oxygen supply system ofclaim 1, further comprising a pressure sensor configured to detect apositive pressure within said face mask.
 6. The oxygen supply system ofclaim 5, wherein said inlet valve is opened immediately upon detectionof a positive pressure within said face mask by said pressure sensor. 7.The oxygen supply system of claim 6, wherein said selected volume ofoxygen is delivered to said reservoir bag prior to inhalation thereof bysaid passenger.
 8. The oxygen supply system of claim 7, wherein saidselected volume of oxygen is delivered to said reservoir bar prior tocompletion of said passenger's exhalation phase.
 9. The oxygen supplysystem of claim 5, further comprising a controller responsive to saidpressure sensor and operative to open and close said inlet valve. 10.The oxygen supply system of claim 9, wherein said controller selectssaid volume of oxygen as a function of cabin pressure altitude.
 11. Theoxygen supply system of claim 1, wherein said source of oxygen comprisesa container of compressed oxygen gas.
 12. An oxygen supply system fordelivering oxygen to passengers in an aircraft in the event of a loss ofcabin pressure, comprising: a source of oxygen; a reservoir bag forreceiving a flow of oxygen from said source; a face mask configured soas to force a passenger wearing said mask to inhale all oxygen that hasaccumulated within said reservoir bag prior to inhaling cabin air tosatisfy the balance of such passenger's tidal volume; and an inlet valvefor preventing the flow of oxygen into said reservoir bag during apassenger's inhalation phase.
 13. The oxygen supply system of claim 12,wherein said inlet valve is opened during a passenger's exhalationphase.
 14. The oxygen supply system of claim 12, wherein said inletvalve is opened for a period of time sufficient to allow a volume ofoxygen to accumulate within said reservoir bag that is less than anaverage passenger's tidal volume.
 15. The oxygen supply system of claim14, wherein said accumulated volume of oxygen coincides to approximatelyone third of an average passenger's tidal volume.
 16. The oxygen supplysystem of claim 12, further comprising a pressure sensor for detecting apositive pressure within said face mask.
 17. The oxygen supply system ofclaim 16, wherein said inlet valve is opened immediately upon detectionof positive pressure within said face mask by said pressure sensor. 18.The oxygen supply system of claim 17, wherein said oxygen is deliveredto said reservoir bar prior to completion of said passenger's exhalationphase.
 19. The oxygen supply system of claim 12, further comprising acontroller responsive to said pressure sensor and operative to open andclose said inlet valve.
 20. The oxygen supply system of claim 19,wherein said controller delays a closing of said valve as a function ofambient cabin pressure.
 21. The oxygen supply system of claim 12,wherein said source of oxygen comprises a container of compressed oxygengas.